Recently there is an increased trend in the papermaking industry to employ more neutral papermaking systems by reducing use of aluminum sulfate. Also often papermaking must be carried out with water of remarkably high hardness caused by increased use of waste paper and extensive employment of the closed water recycle system (in cases where a large amount of CaCO.sub.3 is present as a filler in waste paper), and sometimes the temperature of papermaking system is markedly high.
Conventional rosin emulsion sizing agents are mainly dispersed and stabilized with anionic surfactants and the sizing performance of these sizing agents is markedly lower in papermaking systems as mentioned above. In order to obtain the desired degree of sizing, increased amounts of sizing agents have to be used. Use of excessive amounts of the sizing agent not only raises manufacturing cost but often causes inconveniences in operation such as foaming, formation of pitch, etc. in papermaking systems, and degrades the quality of the produced paper.
U.S. Pat. No. 3,966,654 (corresponding to Japanese Patent Publication No. 58-34509) and British Laying-Open Patent Publication No. 1551645-A (corresponding to Japanese Laying-Open Patent Publication No. 53-12951) disclose some cationic rosin emulsion sizing agents. However, these sizing emulsions are not satisfactory in storage stability and mechanical stability and sizing performance.
The purpose of the present invention is to overcome the above-mentioned defects of conventional rosin emulsion sizing agents, and provide novel useful rosin emulsion sizing agents. We have conducted an intensive study and found that rosin emulsions containing a partially or totally quarternized product of a copolymer of an alkylaminoalkyl ester or alkylaminoalkyl amide of (meth)acrylic (the term "(meth)acrylic" being used to mean "acrylic and/or methacrylic") acid, an alkyl ester of (meth)acrylic acid and/or a styrene compound (meaning styrene or derivatives thereof) are excellent in emulsion stability and exhibit excellent sizing performance when added to papermaking systems of any pH in a wide range from acidic to neutral, and in particular, these emulsions exhibit excellent sizing performance in papermaking systems in which conventional rosin emulsion sizing agents cannot satisfactorily function, that is, in systems of which the pH is almost neutral (that is, containing less aluminum sulfate), the water hardness is high and the temperature is high.